Hi, I had turner test pipes and stage II tune done about 3 months ago. Last week, I reflashed the ecu only eliminating the launch control option which I found useless. Yesterday, I got an increase emission fault code(274a lambda sensor pump current assimilation error vkat bank1) I believe this is referring to a bad pre-cat o2 sensor. I cleared the code but it came back within an hour.

I do recall recently reversing into a parking spot and bump the bottom of my exhaust on the parking space cement block. Any chance, that could have dislodged the sensor and/or piping which caused the CEL?

These o2 sensors + labor is NOT cheap so I'd appreciate your insight on what other quick fixes may exist. It's hard to imagine that the test pipes and tune didn't play a role. this is slowly turning into quite an inconvenience to say the least.

Did you have it tuned for no cats? If yes maybe installer twisted your O2 sensors without disconnecting them during install possibly breaking one of the wires or since you just stated you scraped it on the pavement, it's possible you messed up one of them

No way to diagnose something where you could have damaged a part. If you believe that you damaged something then before we start speculating, it would be best to get the car up and take a look under there although from what you describe it's highly unlikely. You could just have a bad o2 sensor. You don't mention what year your car is.

Definitely an o2 sensor - I had exact same code, tune and test pipe independent in my opinion...I had o2 go before I got test pipes and tune...tried to see if it would just go away after the upgrade but it didn't. Eventually just had to bite the bullet and change out the o2. I didn't notice that much of a drivability difference though between bad and good o2 sensor tbh. There are o2 sensors, there's bank 1 and bank 2. It's kind of opposite to how you'd think - bank 1 is passenger side, bank 2 is driver's side.

Update: I took my car into an indy BMW specialist on Monday for an oil change, brake fluid flush and vehicle check. These were all coming due(I'm at 56k miles) so I wanted to take care everything at once.

Long story short, they didn't have the o2 sensor in stock(though I mentioned this when making the appointment) so I planned to make another appointment for the following week. I picked up the car and drove it to work. As expected, the increased emission light was still on and the car felt fine. On the way home from work, I pushed the car a little on the highway and it definitely felt sluggish at high rpms. I stopped for gas and when I started it up again, the fault did not return. "All Systems OK"

I've driven maybe 50-60 miles since and the light has not returned and although the power seams to be coming back, it's not quite where it was before taking it to the shop. The mileage seems normal so I'm planning on waiting until the next time I need to get my car serviced(spark plugs, oil change) to change out the o2 sensors, or when the SES-increase emission warning light returns

Update: I took my car into an indy BMW specialist on Monday for an oil change, brake fluid flush and vehicle check. These were all coming due(I'm at 56k miles) so I wanted to take care everything at once.

Long story short, they didn't have the o2 sensor in stock(though I mentioned this when making the appointment) so I planned to make another appointment for the following week. I picked up the car and drove it to work. As expected, the increased emission light was still on and the car felt fine. On the way home from work, I pushed the car a little on the highway and it definitely felt sluggish at high rpms. I stopped for gas and when I started it up again, the fault did not return. "All Systems OK"

I've driven maybe 50-60 miles since and the light has not returned and although the power seams to be coming back, it's not quite where it was before taking it to the shop. The mileage seems normal so I'm planning on waiting until the next time I need to get my car serviced(spark plugs, oil change) to change out the o2 sensors, or when the SES-increase emission warning light returns

I think you're doing yourself and the car a disservice by driving it with a preexisting o2 sensor issue (especially for pre-cat). You should change that sensor as soon as possible and not wait for the light to return.

Feedback from the pre cat o2 sensors are essential to fuel mixture correction - which means that if not reading properly that it can cause loss of power, poor consumption, lean conditions, etc.. I would suggest taking care of it before your service.

Kind of off topic but what a wierd thing to code out-the LC. I mean if you don't like it why don't you just not engage it? Its not like it comes on automatically and its actually kind of cumbersome to use anyway. Kind of bizarre what people think of.

In terms of the pre-cat 02, while it is the "primary" sensor used, the post-cat O2 or secondary O2 "checks" what the primary did and if it was lean or any problems occured the secondary would light up and throw a code so I am not saying don't fix your primary sensor but its certainly not going to run lean or pose any danger with secondary intact

In terms of the pre-cat 02, while it is the "primary" sensor used, the post-cat O2 or secondary O2 "checks" what the primary did and if it was lean or any problems occured the secondary would light up and throw a code so I am not saying don't fix your primary sensor but its certainly not going to run lean or pose any danger with secondary intact

No. This is not how it works at all. Where do you get this information from?

bmobile - I have basically the exact same fault as you with one of my pre-cat 02 sensors. I ordered the new sensor from ECS (148 bucks) 1 1/2 weeks ago and it showed up via Fedex yesterday. I plan on installing it tonight in my garage using some jack stands. From what I've read, it's not that hard of a job...as long as you can get under there, remove the metal shield, the sensor should be removable with a 22mm wrench. I'll report back after I complete the job and let you know how it goes.

bmobile - I have basically the exact same fault as you with one of my pre-cat 02 sensors. I ordered the new sensor from ECS (148 bucks) 1 1/2 weeks ago and it showed up via Fedex yesterday. I plan on installing it tonight in my garage using some jack stands. From what I've read, it's not that hard of a job...as long as you can get under there, remove the metal shield, the sensor should be removable with a 22mm wrench. I'll report back after I complete the job and let you know how it goes.

Job complete...not too bad. It was helpful having a second set of hands, but not required. I think it took us about 45 minutes to do the job...we weren't in a hurry and took our time. The hardest part was getting the wire from the sensor off of the little clip that holds the wire up. Just hard to reach, but really wasn't all that bad.

I can't imagine paying a shop to do this...All you need is a 22mm open end wrench, a floor jack and some jack stands. Piece of cake.

I've driven the car about 50 miles since the change last night...no CEL yet. (I cleared the fault codes last night after the install). Keeping fingers crossed that this did the trick.

Update: I took my car into an indy BMW specialist on Monday for an oil change, brake fluid flush and vehicle check. These were all coming due(I'm at 56k miles) so I wanted to take care everything at once.

Long story short, they didn't have the o2 sensor in stock(though I mentioned this when making the appointment) so I planned to make another appointment for the following week. I picked up the car and drove it to work. As expected, the increased emission light was still on and the car felt fine. On the way home from work, I pushed the car a little on the highway and it definitely felt sluggish at high rpms. I stopped for gas and when I started it up again, the fault did not return. "All Systems OK"

I've driven maybe 50-60 miles since and the light has not returned and although the power seams to be coming back, it's not quite where it was before taking it to the shop. The mileage seems normal so I'm planning on waiting until the next time I need to get my car serviced(spark plugs, oil change) to change out the o2 sensors, or when the SES-increase emission warning light returns

Just because the SES no longer shows up does not mean the problem is gone. As long as you have a fault stored in the DME the problem exists. You can have an 02 go bad and the SES will activate but not always be present. Driving the car with a bad 02 sensor is a big no no.

Damn, $115 for the same Bosch sensor I bought for $147. That's a heck of a price. Well, when the other side fails I guess I know where to buy it! I never thought of buying an O2 sensor on Amazon...I guess they pretty much carry everything now. ;-)